In the construction of printed circuit boards and other circuitry involving digital integrated circuits (hereinafter referred to as ICs) many manufacturing defects will occur due to poor connections, bad soldering techniques and the like. These defects must be located and corrected before the products are shipped to customers and the process of testing the same requires fast testing techniques as well as equipment that is simple to use and of a size permitting mobility even in limited spaces. The prior logic test units have not met all of the foregoing criteria for one reason or another; therefore, a need has arisen for such a test unit which is simple to use, can be hand-carried, and can operate to test an IC while the same is in-circuit.